Detonation measurement



8% 21, 1943. K, R ELDREDGE 2,337,522

' I-JETONATION MEASUREMENT Filed May 4, 1943 2 Shets-Sheet 1 BNVENTOR H]R Eidk edge Keane Dan E, 143. K. R. ELDREDGE 2,337,522

DETONATION MEASUREMENT File'd May 4, 1943 2 Sheets-Sheet 2 Dercnafionickup ompur Valvnqise V M F162 I i 5' I M v ncom n lgna mpii'fied inmeiering I Vaiw noise Diffeireni-aal ed +6 suppress low fiequehcies inme'fering circuh Pamially in+egra+eoi signal in lockingcircuif ,5; gq eimpuls in liQckin cir'cuh l I g i sigmai %o final mel er'in I c3 INVENTQKenv R. Kid Fade in the engine cylinder.

Patented Dece2l, 1943 UNITED "STATES PATENT? OEFICE .Kenneth R.Eldredge, Berkeley, Calif., assignor to Standard Oil Company orCalifornia, San Francisco, Calif., a corporation of Delaware ApplicationMay 4, 1943, Serial No. 485,626

5 Claims. 401. 117-351) This invention relates to a means fordetermining the intensity of detonation in the cylinders of internalcombustion engines, and particularly refers to means whereby themeasurement is made only during the actual combustion period of theengine cycle.

This invention .is particularly adapted to utilize the alternatingvoltage output of the detonation indicator which is the subject of myPatent No.

2,269,760, issued January 13, 1942. That device utilizes amagnetostrictive element which is stressed by pressure variations in anengine cylinder and correspondingly'modifies the magnetic fluxpassingthrough a coil to produce an alternating current voltage whichfaithfully represents at any instant pressure gradient conditionsexisting The output from such'a pickup unit or-indicator can beconsidered to consist of a relatively low-frequency alternating currentimpulse due to the pressure change in the combustion chamber on which issuperimposed relatively high-frequency waves of the detonation effect.Inaddition to this output, vibration from valve operation or othermechanical effects, which take place before and after'the pressureimpulse due to combustion, give high-frequency responses whichfrequently have similar characteristics to those produced by detonation.In order to lock out such extraneous responses from the'quantitativmetering function of this invention, an arrangement has been perfectedwhich renders a portion'of that circuit nonconducting except at suchtime that the combustion pressure is impressed 'upon the pickupapparatus. De-

ment in a metering circuit to largely eliminate the pressure component.A separate circuit which can bedesignated'a locking circuit is providedin which the pressure gradientdiagram is integrated and used to providethe means of unlocking the metering circuit or rendering the latterresponsive only during the combustion period in the engine The humanear, which has here,-

cylinder at which tlme the detonation effects are to be measured.

Heretofore those devices which have had a similar object, that is toprevent the effect of extraneous noises upon a detonation responsivemeans. have used mechanical vibrations set up in the body of thecylinder of an engine to pick up detonation vibrations and haveattempted to limit the time of such indications by synchronizing theindicator withan impulse from the ignition system. 7 Such an arrangementis that of the-Lancer Patent No. 2,291,045. These devices, however, give.no quantitative results and consequently are not usable wheresuccessive tests are to be made on fuels, for example, to determinetheir knocking characteristics. In other words, they will indicate thepresence or absence of detonation but give no reading of the intensitythereof.

Other objects and advantages of this invention will be apparent from thefollowing description and from the accompanying drawings whichillustrate a preferred embodiment together with a' series of curvesshowing the effects of variousportions of the metering and lockingcircuits upon Referring to .Figure 1, reference numeral 10 designates adetonation pickup unit uch as that of my Patent No. 2,269,760 previouslymentioned, in which a coil or other means are provided to givealternating current responses to pressure changes within the combustionchamber of an internal combustion engine. The output of pickup unit Itpasses through an attenuator l I provided with a number of fixed or steppositions and a line adjustment l2. From the attenuator the outputpasses through lead l3 to the grid 14 of a first amplifier triode i5having a cathode l6 heated by conventional means (not shown) and a plateIT. From the plate I! the metering circuit extends through lead 18through a conventional resistance coupling composed of condenser l9 andresistor 20 to the grid 21 of a second amplifier triode 22 having aconventional cathode 23 and plate 24. Cathode 23 is heated in the usualmanner and is normally biased positively by the looking circuit tube IIwhen that tube is passing current. This positive bias is set up by thedrop across resistor 13 and makes cathode 23 sufliciently positive withregard to grid 21 to cut of! tube 22.

The output of triode 22 is passed through lead 2a through a conventionalresistance coupler composed of a resistor 26 and a small condenser 21. Asecond resistor 28 is adapted to cooperate with condenser 21 todifferentiate the amplified signals coming from triode 22 (Figure 3) byby-. passing to ground -lead 29 the low-frequency pressure wavecomponent. This will result in a diagram substantially as that of Figure4.

When the cathode 23 of triode 22 is made less positive so that saidtriode can act as an amplifier, the difi'erentiated signal is passedthrough lead 30 to the cathode 3| of a diode half-wave rectifier 32. Therectified voltage from plate 33 The output from plate 44 of pentode 39passesthrough lead 45 to a Wheatstone bridge circuit generallydesignated 46 in'which is connected a current measuring means such as amilllammeter il having an appropriate shunt 48.

The locking circuit mentioned above which pre vents the operation of thesecond amplifier triode 22, except at such times as the combustion cycleis actually taking place in the engine cylinder, receives the sameamplified signal as does the metering circuit just described from platell of the first amplifier triode l by means of lead to. series resistor5| and condenser 52 to ground lead %3. This acts to bypass to ground thehighfrequency components of the amplified signal so that thelow-frequency pressure wave component (Figure 5)'is impressed upon thegrid 56 of the triode amplifier 55. That amplifier is provided with aconventional cathode 56 and a plate 5".

The amplified and partially integrated signal is passed from plate 5'!through lead 58 to a resistor coupler composed of resistor 59 andcondenser 60 and through a second partial integrating circuit composedof resistor 61 and condenser 52. The integrated amplified signal thenpasses .to grid 63 of a second amplifier triode E i having aconventional cathode 65 and plate 65. The characteristics of this tubeare chosen so that substantially a square wave impulse is passed fromplate 66 through lead Bl to a resistance coupler composed of condenser68 and resistor H immediately becomes conducting, thereby increasing thepositive bias on cathodes l2 and 2t and making grid 2i of tube 22 sonegative that In the example of Figure l a conventional power supply,consisting of a transformer 1t, full-wave rectifier-Ti and voltageregulator 78 with the usual filters and voltage divider 81, isillustrated. Obviously this could be rep aced y any suitable sources ofdirect current. It is desirable that the movable tap 19 of a Wheatstonebridge 46 be connected at an intermediate point 80 in the voltag divider8|. It has been found that variations in individual characteristics ofthe final metering amplifier pentode 39 may be such that the connectionof point 80 into the voltage divider can be chosen in such a manner thatvariations in voltage which would. otherwise afiectthe consistency inoutput of pentod 39 may be compensated.

Although a single example of this invention has been described andillustrated, it is obvious that numerous modifications and changes couldbe made without departing from the invention I and all suchmodifications that come within the This signal is partially integratedby the 69 to the control grid 10 of a pentode amplifier ii. Pentode IIis provided with the usual cathode 12 having a bias resistor 13, thelatter being so chosen that when pentode I! is in its normal condition,namely a conductor for current between cathode l2 and plate It, thepositive bias on that cathode, which is connected by means of lead 15 tothe cathode 23 of the second triode amplifier. 22 of the meteringcircuit, will be of such a value that triode 22 will not act as anamplifier. The operating characteristics of pentode II are so chosenthat when the substantially square wave impulse (Figure 6) is impressedupon control grid 10 that tube becomes nonconducting which permits thebias on cathodes l2 and 23 to become less positive, thereby permittingtube 22 to become an amplifier and to pass on to the scope of theappended claims are embraced thereby.

I claim:

1. Apparatus for measuring the average intensity of detonation in aninternal combustion englue in which there are means responsive topressure variations in the engine combustion chamber, said means havingan alternating current voltage output signal which includes a detonationfrequency superimposed upon a pressure wave frequency, comprising ametering circuit including means for amplifying the output of saidpressure responsive means, said amplifying means having at least onecathode, means for difierentiating said amplified output to suppress thepressure wave frequency component thereof, means for rectifying saiddiiierentiated signal, an amplifier for said rectified signal and ameter for measuring the average amplitude of said rectified andamplified signal; a locking circuit, means in said locking circuit forreceiving the signal output of said pressure responsive means, means insaid locking circuit for integrating said amplified signal to suppressthe detonation responsefrequency thereof andto modify said signal to asubstantially square wave impulse, an amplifier in said locking circuithaving a cathode, said cathode being in parallel with the cathode orgrid return of an amplifier in said metering circuit, and biasformlngmeans for said cathodes, so constructed and arranged thatsaid squarewave impulse from a given ressure and detonation response signal willcause said amplifier in said metering circuit to be operable only duringthe duration of said given pressure wave impulse, whereby the currentdue to detonation frequencies will pass through said metering circuitand be indicated on said meter.

2. Apparatus according to claim 1 with the addition of means in saidmetering circuit for introducing a time delayfor said rectified signal,so t'onstructed and arranged that said meter will read the average peakintensity of'the rectified detonation frequ ncy urrents as averaged over3. Apparatus for measuring the average intensity of detonation in aninternal combustion signal; a meter for measuring the average amenginein which there are means responsive to plitude of the resultant directcurrent impulses:

means for differentiating the alternating current sure wave. voltagesignal to remove the pressure wave fre- 5. Apparatus for measuring theintensity of quency component and an amplifier for the al- 1 detonationin an internal combustion engine on remove the detonation responsefrequency there- 15 quency detonation component superimposed uponpressure wave frequency for periodically removnent, comprising ametering circuit, differentiatmg the bias from said metering circuitampiifier,. ing means in said circuit for making it; responand means formetering the differentiated detosive only to the detonation frequencycom nation frequency component of said signal. 20 nent, a normallyinoperative amplifier in said unit comprising a low frequencyalternating cur- 25 bustion pressure component, means responsive to rentimpulse due to combustion pressure on which said single impulse forrendering said metering

